Chapter 7 Summary Part 1: Energy Solutions by Rector and Yu, Climate Change for Astronomers

These are molecules made of hydrogen and carbon, and include coal, petroleum and natural gas, that formed from the remains of decomposed organic matter such as plants that have been subjected to millions of years of high pressure and temperature (I was disappointed to find out that the idea they come from dinosaur remains is basically a myth). Their chemical potential energy is released into thermal energy via combustion with oxygen, which can be used for heating or to produce electricity by rotating a turbine.

Pros: 

• They are readily dispatchable and thus convenient (although in extreme weather events they can be less so). 
• They have a high specific energy.

Cons: 

• They contribute to climate change by producing GHGs from their combustion, particularly CO₂, which traps heat in the planet’s atmosphere. Fossil fuels emit the highest amount of CO₂ over their lifetime out of all the energy sources that will be discussed in this summary (for natural gas, oil and coal the figures are 486, 840 and 1001 kg CO₂/kWh respectively). By burning fossil fuels, we are releasing, in only a few hundred years, carbon which has been sequestered over millions of years by the Earth, and we can expect in only a few hundred more, the supply will be depleted if it is continuously consumed at the current rate. 
• Abandoned wells from mining of fossil fuels continue to emit methane gas that is as potent as CO₂ for trapping heat in the atmosphere. 
• There is a long list of health effects from hydrocarbons – combustion of fossil fuels produces sulphur oxides, nitrogen oxides, particulates and heavy metals that are associated with health conditions including asthma, breath difficulties, brain damage, heart problems, cancer, neurological disorders and premature death. Exposure to particulate-matter is also associated with reduced life expectancy. The pollutants can end up in the ocean and in fish we eat, create acid rain, and contaminate waterways; environmental damage can also occur from fracking rocks to access the fuels, and it is thus banned in some countries. 
• Fossil fuels can also be subject to large price fluctuations in changing market conditions. They are also linked to violence in low-to-middle income countries who have these natural resources.

Biomass includes plants or wood that are burned directly (e.g. for cooking or heating, especially so in developing countries) or used to make biofuels (e.g. bioethanol or biodiesel), which can potentially be used as a substitute for, or mixed with fossil fuels for various sectors, e.g. for engines for transportation. 

Pros: 

• Biofuels have less CO₂ emissions than fossil fuels, and they are a kind of renewable energy. 
• They can be mixed with other fuels in the transportation sector, to reduce CO₂ emissions (in which it will otherwise be difficult to switch to cleaner energy solutions). Because of this, some see biomass as a ‘transition’ fuel.

Cons: 

• It is disputed as to whether the energy cost to produce biofuels by harvesting crops, processing them and transporting them is less than the energy gained from the fuel. But due to the fact it has a low specific energy (about 40% less than petroleum), it tends to be less efficient than other fuel sources. 
• The CO₂ that is released from the production and combustion of biofuels does not totally balance with the CO₂ that is absorbed from photosynthesis in growing crops to produce biofuels, so they do not offset CO₂ emissions. 
• While biofuels produce less air pollution than fossil fuels, if they were to be more widely used they will impact land use which could otherwise be used for agriculture, timber, nature conservation and natural carbon sequestration. 
• The cost of biofuels can also fluctuate dramatically like fossil fuels, especially if there is seasonal variability for the crops used to produce them (e.g. corn). 

There is a lot of potential for solar energy as it is low cost, has low emissions, and is renewable. Given that the cost of solar is constantly decreasing and the technology is continuing to improve, the U.S. Department of Energy expects that solar energy will account for 40% of the electricity market by 2035. Solar energy technologies include photovoltaics (PVs) that convert the radiation directly to electricity via the Photoelectric Effect, or solar thermal power, which involves heating a material via sunlight and then storing the thermal energy.

Pros: 

• On average 170,000 TW of solar radiation hits the Earth continuously – it’s renewable! 
• Solar energy doesn’t require transport, reducing maintenance and operations costs relative to other energy sources. It is tied with wind power to be the lowest cost source of electricity. In fact, it may be financially preferable to decommission some coal power plants before they reach the end of their lifetimes and replace them with solar. 
• They do not produce any GHGs – although producing solar power does contribute 28 kg CO₂/kWh (e.g. due to the manufacturing of panels).
• Solar panels can be placed on ‘unusable land’ such as in urban areas, contaminated land, landfills, etc (such that there is minimal environmental damage by placing a solar farm in the location). While solar farms require a lot of land and can impact the environment, it may be possible to combine solar farms with land used for crops that require shade, livestock or other purposes. 
• Solar panels take only about 3 years to produce enough energy to compensate for that required to produce the panels, well within their 25-30 year life span. 
• While installation of solar panels in a home can be expensive, residents can be compensated for excess energy produced that is returned to the grid, and the installed panels can increase the resale value of a home. 

Cons: 

• Solar energy is not as readily dispatchable as fossil fuels due to variability of the weather or region, so it will need to be combined with other energy sources in order to replace fossil fuels as they are used now. Likewise, solar energy production peaks around midday, while the greatest demand for energy is generally towards the evening. 
• Solar panels have historically been produced with minerals including cadmium, copper and silicon, and when the panels are disposed of they contribute to pollution; cadmium for example, is a toxic chemical. However, the technology is constantly improving and now requires less of these materials than before. The effects of pollution are also – even now – far less than that of the long list of effects by using fossil fuels. 
• Airborne particulate matter (such as in regions where the air pollution is high) or shade significantly reduces the energy output of solar panels, in a way that is not proportional to the area of the panel that is shaded. However, new designs are also aiming to overcome these issues. 

Wind power involves using wind to spin turbines to generate electricity.

Pros: 

• Like solar, it has great potential because it does not produce GHGs during operation (they contribute just 13 kg CO₂/kWh from production of turbines).
• Wind turbines do not consume fuel.
• Wind energy is cheap to produce. The maintenance costs are less than half of that for coal generated power.
• It is possible to build wind turbines offshore (turbines placed in water, usually shallow) where the wind is more consistent and the rotors can be built to be larger. This allows for more efficient electricity generation (although bringing the electricity back to shore presents a challenge). 
• It is expected that wind power has a potential global capacity of 250 TW, 10 x greater than the current global energy demands. It is a misconception that the energy required to build a wind turbine is greater than what the turbine will ever generate; wind turbines ‘pay back’ their GHG emissions in less than a year and can operate for up to 20 years. 
• Wind power is expected to dominate in the future – the sector has already increased 4-fold in its energy output over a 10 year period and the International Renewable Energy Agency (IRENA) expects global deployment of wind to increase 10-fold by 2050.

Cons: 

• Wind farms can take up a lot of space and are sensitive to the weather. 
• Wind power produces low frequency noise that may affect the environment. 
• There is some risk to injuring wildlife via bird collisions, although this is much less likely to happen if the turbines are painted with dark colours on one side of the rotor. 
• Wind turbines are not fully recyclable, but the waste from decommissioned turbines is still 200 times less than that of coal generated power.

Nuclear fission energy is produced from the decay of a heavy radioactive atom (usually Uranium-235) in nuclear reactors. When the atom decays to a lower mass nucleus, energy is released that heats up water and produces steam that spins a turbine to generate electricity.

Pros: 

• Nuclear fission does not create CO₂ during operation (over its lifetime it contributes 13 kg CO₂/kWh from production of plants). 
• Nuclear fission is extremely energy dense. A single kilogram of Uranium-235 can produce the equivalent energy of nearly 3 million kilograms of coal. 
• It is also quite dispatchable and has a high capacity factor.

Cons:

• Nuclear is not extremely adaptable to rapidly changing demand as the reactors require a few hours to start up. 
• Due to disasters which involved catastrophic failure of the reactors like those in Chernobyl or Fukushima, they are perceived as unacceptably dangerous and not favoured politically. This is also in addition to the misconception that they release radiation from the reactors themselves. Instead, you may be at more risk of health effects of radiation exposure from airborne particulate matter released from coal-power plants than that of a nuclear power plant!
• Nuclear reactors do however, produce dangerous radioactive waste that needs to be stored properly; the toxic waste remains radioactive for tens of thousands of years and needs an appropriate storage location. 
• The mining of uranium can be dangerous because of the risk of radioactive dust being blown into civilian areas (in addition to the normal safety hazards associated with mining). Radon gas is also a dangerous byproduct of decaying uranium which poses a risk to those mining it and requires for the uranium to be stored appropriately. 
• Nuclear power plants have the potential to be targeted for malicious purposes. There is also some risk that nuclear power plants can be exploited, because it is possible to use plants developed for peaceful electricity generation to produce Plutonium-239 which is used in nuclear weapons. 
• The cost of uranium, a volatile commodity, can make nuclear power plants a risky financial investment. Furthermore, building new nuclear power plants or even decommissioning plants is expensive.

Hydroelectric energy uses flowing water to spin turbines and produce electricity. Usually water is directed from a reservoir (such as a dam) through turbines.

Pros: 

• Running a hydroelectric plant does not produce CO₂ during operation (over its lifetime it contributes 21 kg CO₂/kWh from construction, etc). 
• It has a highly dispatchable output since the energy output depends on the flow rate of the water, allowing it to be adjusted very quickly (on time scales of minutes). 
• The dams built for these facilities can also provide flood protection and security. 
• Operational and maintenance costs of hydroelectric energy are quite low.

Cons:

• During times of drought it can be a less reliable energy source; there is some seasonality in the power output which peaks around spring when winter snow caps melt. Thus the plants need to be built in locations with appropriate resources. 
• The cost of building a hydroelectric plant can vary and typically are somewhere between the costs for wind/solar and the low end for nuclear (they are potentially expensive).
• Hydroelectric plants that use water from dams or reservoirs need to compete with water demand for other needs (such as requiring the water for agricultural purposes) and can have significant impacts on fish migration. The dams that are built (such as on rivers) can affect aquatic ecosystems due to changes in water temperature, chemistry and natural flows. The risk of flooding from dams can also impact biodiversity, and, in some cases, it is reported this damage is greater than that of the reductions of GHG emissions. 
• While the hydroelectric generation itself doesn’t generate emissions, microbes on the bottom of the dams can produce methane which do create emissions. 
• Since the dams can affect water quality and agriculture, local communities can be impacted and hydroelectricity is becoming less popular.

Geothermal energy uses the heat from the Earth to heat water and spin a turbine to generate electricity. Water is injected into a well and brought back up after heating. Geothermal energy has been used for heating and for agricultural and industrial purposes (e.g. warming greenhouses). Typically, this energy is acquired in places where there is geological activity close to the surface of the Earth, such as from volcanoes or geysers. It is difficult to attempt to extract geothermal energy from deeper in the Earth, but research is underway to attempt to try to overcome this.

Pros: 

• Geothermal energy is able to produce energy with no CO₂ emissions and very little pollution during operation. It is an unlimited energy source from a practical point of view. 
• The plants are very physically compact. 
• The plants have no dependency on the weather to produce energy. 

Cons: 

• The costs of geothermal power plants remain a challenge, although they are less expensive than nuclear power. 
• The power output of geothermal plants can be affected by the levels of volcanic activity in nearby areas which can impact the temperature and flow rate from the source. 
• Geothermal power plants require more maintenance than most other renewables. 
• While there is research into fracking for expanding the range of locations where geothermal power plants can be built, much like oil and gas drilling this has been associated with small earthquakes, and there is risk of contaminating groundwater sources.

Hydrogen energy involves combustion of hydrogen to produce heat or alternatively involves hydrogen fuel cells – an electrochemical device to produce electricity from hydrogen and oxygen. The fuel cells involve separating hydrogen ions (protons) from electrons; the flow of the electrons gives the generated electric current.

Pros: 

• Hydrogen energy may be attractive for storing energy for later use, since excess energy produced from other renewables can be stored in the hydrogen fuel cells. This means it could potentially replace fossil fuels in combustion engines, and be suitable for the transportation sectors that rely on fossil fuels now.
• If the hydrogen is produced from electrolysis, it doesn’t generate CO₂ emissions and it is renewable. 
• There is some growing evidence that hydrogen may be naturally occuring underground that could be used to meet global energy demands.

Cons: 

• While combusting hydrogen does not produce CO₂, any kind of burning will generally produce nitrous gases. 
• Hydrogen fuel cell storage contributes about 38 kg CO₂/kWh, since not all hydrogen is ‘clean’ such as that produced from electrolysis; it may be (and most of it is) produced from fossil fuels. 
• While combusting hydrogen could be used to replace burning coal or fuel (especially for energy sectors that cannot be electrified easily), hydrogen has a far lower energy density than that of coal so it requires far more to be burned. 
• There are potential safety risks with hydrogen, because hydrogen leaks are odourless and colourless and hydrogen is highly flammable. 
• Hydrogen energy is expensive to produce and to store. The high storage costs are due to the fact that it must be stored at very high pressure or at cryogenic  (very low) temperatures. The storage of hydrogen also means that shipping and transport of hydrogen and fuel cells is required which adds to costs.
• The conversion of energy to hydrogen storage and back reduces the total energy available from this source to 30% of the initial energy available, so some energy is lost in storing hydrogen.